1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier or a laser printer having an electrophotographic process.
2. Description of the Prior Art
Generally, the electrographic copying apparatus coronaelectrifies by an electrification charger the surface of a drum-like photosensitive member so as to form uniform electrostatic charge distribution, eliminate the electrostatic charge by a reflection light corresponding to the information to thereby form electrostatic latent images, the latent images are developed by a toner and thereafter transferred to a copying paper and fixed thereon by a heating roller. In order to transfer the images to the copying paper, a transfer charger is adapted to be applied to high voltage of several KV to thereby electrify the rear surface of copying paper and in order to separate the copying paper from the photosensitive member, AC voltage of several KV is adapted to be applied on a separation charger.
In such copying apparatus, however, after a large number of papers (copying papers) of the same size are copied, when a copying paper of larger size is used for copying, the range of the size of the former copying paper becomes slightly black, that is, the so-called paper size memory phenomenon or filming phenomenon, the black portion being called a fog. It is considered that the fog is created by deterioration of the ability to remove the charge by the light at a portion where talc or the like included in the paper attaches to the photosensitive member. As the countermeasure for the above, it is proposed that an erasing corona charger separate from the separation charger is provided and used to remove electricity from the photosensitive member and a cleaner blade for removing residual toner is used to scrape off the attachment. Such a method, however, must be provided with the erasing corona charger for removing charge only, so that it is very difficult to contain such that the charger in a restricted space around the photosensitive member and a new exclusive power source must be provided, thereby creating the problem in that the apparatus is large-sized. Also, it is proposed that a pressing force of the cleaner blade applied on the photosensitive member be increased to scrape off the attachment together with the residual toner, in which the life spans of cleaner blade and photosensitive member are reduced, resulting in lack of practicability.